Hi Civ folks!
First of all, thanks to Bad Ronald for a mod well done - and to all the other modders in this forum as well who keep this excellent game getting even better.
I followed your discussion about a "proper" German flag replacement and since I found some comprehensive information about both the black-red-gold and the black-white-red tricolor flags on
http://www.deutsche-kaiserreich.de/ - I thought I'd translate the stuff they wrote on their website from German to English. Even myself, as a native German living in Frankfurt am Main, learned a lot reading this. Comments in brackets have been added by myself for the sake of clarity:
Black-red-gold flag:
Black-red-gold is the older German flag. The origin of the colors is the uniforms of the "Lützower Freikorps", a corps of volunteers who fought under the leadership of the Prussian Major Adolf von Lützow against French occupation in Germany in 1813. (It was also in this year when the Iron Cross or "Eisernes Kreuz" was invented by Frederick William III of Prussia, as a decoration for bravery in the fight against the French.) The corps' uniforms were made up of black and red tunics with golden buttons. (Note that it is nevertheless true that black and gold were also the colors of the ancient Holy Roman Empire during the Medieval.) On June 17th 1813, the corps was ambushed by the French at Kitzen near Leipzig, and was almost completely annihilated. On June 12th 1815, seven students who had served in the corps, together with other nationalist students, founded the Fraternity of Jena ("Burschenschaft zu Jena" - the first German student league). They chose black-red-gold to be the colors of the fraternity. Excerpt from the constitutional charter (translated): "To commemorate the fact that despite all the joys of youth, the seriousness of life is to be kept in mind, they chose red and black as the colors of their banner."
On October 18th 1817, the fourth anniversary of the Battle of Leipzig ("Völkerschlacht bei Leipzig" - defeat of the remnants of Napoleon's army withdrawing from the Battle of Moscow), about 500 students of the fraternity and some professors from all over Germany went to the Wartburg near Eisenach (the same castle where Martin Luther translated the Bible to German during his exile). Their intend was to demonstrate for freedom and a unification of all German states, waving red-black-red flags (only the fringes were golden at that time). (Note: as opposed to the United States, where the term "liberal" has a somewhat different meaning, these were the founding days of liberalism in Germany. Being a liberal in Germany at that time meant to oppose the hierarchic order of Germany's split-up monarchies and aristocracies, struggling to replace them by a republic, a unified German nation. At that time, the monarch rulers of the independent German states suppressed and prosecuted such movements as they feared the loss of their political power.)
At the Hambach Convention ("Hambacher Fest" - May 27th-May 30th 1832), 30.000 participants demonstrated for nationalistic and democratic goals and, for the first time, used a black-red-gold tricolor flag. In the middle red stripe the words "Deutschlands Wiedergeburt" (Germany's rebirth) were clearly showing the demand of the crowd - the formation of a unified German state. On May 18th 1848, the representatives of the first German national assembly gathered in the Paulskirche church in Frankfurt am Main. On November 13th 1848, the black-red-gold flag was proclaimed to be the German flag. Moreover, the flag was used as a naval ensign by the German Confederate Navy ("Deutsche Bundesmarine") 1848-1852. In the German War ("Deutscher Krieg") of 1866, Austria and her allies fought under that flag against Prussia and her allies.
Today, black-red-gold is a symbol for the German democracy. In the German Empire ("Deutsches Reich"), these colors were the state flags of the principalities of Waldeck, Reuss Younger Line and Reuss Elder Line. From 1919 until 1933, the black-red-gold flag once again became the national flag of Germany. The new social democratic government deliberately chose the old colors black-red-gold to represent the first German republic, to dissociate (the new state) from the old (Imperial) system and its symbols (the black-white-red flag). At that time, this was supposed to make it easier for Austria to unify with Germany (which never happened until 1938, when Hitler annexed Austria by force), as the Germans in Austria-Hungary also used black-red-gold as their flag. Since 1949, it was the national flag of both German states (Federal Republic of Germany - "West Germany" / German Democratic Republic - "East Germany"). (In 1956, the East German flag was officially altered to carry additional, socialist symbols in a centered crest, consisting of a hammer, compasses and grain - symbolizing workers, academic persons and farmers. Since the re-unification of both German post-WWII states in 1990, the plain black-red-gold flag is, again, the national flag of Germany.)
Black-white-red flag:
Today, it is often implied that Bismarck's anti-democratic attitude was the reason for (his) rejection of black-red-gold (as the colors of the North German Confederation). The true reason probably is the German War of 1866 ("Deutscher Krieg" - Prussia and her allies against Austria and her allies), where the troops loyal to the German Confederation ("Deutscher Bund" - Austria, Saxonia, Bavaria, Wurttemberg, Hanover, Hesse-Darmstadt, Baden, Saxe-Meiningen, Hesse-Nassau, Reuss Elder Line, and Frankfurt), under leadership of Austria, used that flag as their banner, which incorporated those ancient German colors. Therefore, it is understandable that Bismarck didn't want to use the war flag of (Prussia's) former enemies as the new flag of the North German Confederation ("Norddeutscher Bund" - all German states except Bavaria, Wurttemberg, Baden, Austria - led by Prussia, founded in 1867), and so he decided in favor of black-white-red. This new flag (black-white-red) was chosen as the symbol of the North German Confederation because it merged the Prussian colors (black-white) and the colors of (most) Northern German states and cities (white-red), as well as to demonstrate the tradition to the Hansa city states (including the city of Bremen). In the Franco-German War of 1870/71, the troops of the North German Confederation fought under that new flag (black-white-red) [...]. After proclamation of the German Empire ("Deutsches Reich") in 1871, black-white-red became the official state flag until 1919.
The Germans strongly identified themselves with the new colors and numerous patriotic songs were composed to glorify them, as the old desire for a unified state was achieved under this flag. The gratification and pride to have decisively beaten (Germany's) old rival, France, as well as the Empire's increased (military) strength and (political) power influenced this strong relationship to the national symbols of the (new) German Empire. For instance, whenever Germany claimed a new colony (during the Age of Imperialism that was to follow), this was symbolized by raising the Empire's flag ("Reichsflagge"), which is documented on many paintings and pictures. In 1914, hundreds of thousands of volunteers marched into war under the black-white-red flag with enthusiasm, as they believed to be home again by the time when the leaves would fall in Autumn. Nobody could really imagine the horrors of war that were to come. The Germans were convinced at that time, that the German Empire had been (deliberately) forced into this war by its enemies. [...].
Many of those, whose comrades senselessly died in the battlefields of World War I, didn't quite understand why exactly those colors, for which they had fought for such a long time, were not going to remain on the flag of the German Empire (after the armistice) in 1918. The new social democratic government deliberately chose the old colors black-red-gold to represent the first German republic, to dissociate (the new state) from the old (Imperial) system and its symbols. At the same time, this was supposed to make it easier for Austria to unify with Germany, as the Germans in Austria-Hungary also used black-red-gold as their flag. During the whole time of its existence, the so-called Weimar Republic ("Weimarer Republik" - 1918-1933) there were disputes about the flag. Black-white-red (even) remained the merchant flag of the Weimar Republic, and since 1926, (the old flag) even became an additional flag of the foreign embassies of the German Empire in 1926 by an official order of (President) Hindenburg ("Flaggenverordnung"). In the first years of the Third Reich ("Drittes Reich" - inofficial term commonly used for Germany during the time of Nazi rule), the old black-white-red flag was used in parallel to the swastika flag ("Hakenkreuzfahne") until 1935 (official order from March 12th 1933). Until today, the reputation of the black-white-red flag is heavily damaged by that fact, as well as due to its wide-spread use by Neonazi organisations (who use it because the display of the swastika is strictly forbidden in Germany).
I hope I don't get punished by the admin for such a long post...

Cheers!